Wireless communication systems are widely used to provide voice and data services for multiple users using a variety of access terminals such as cellular telephones, laptop computers and various multimedia devices. Such communications systems can encompass local area networks, such as IEEE 801.11 networks, cellular telephone and/or mobile broadband networks. The communication system can use one or more multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and others. Mobile broadband networks can conform to a number of standards such as the main 2nd-Generation (2G) technology Global System for Mobile Communications (GSM), the main 3rd-Generation (3G) technology Universal Mobile Telecommunications System (UMTS), the main 4th-Generation (4G) technology Long Term Evolution (LTE) and emerging 5th-Generation (5G) technologies.
A wireless network may include a wireless device and a plurality of base stations. The wireless device may be a notebook computer, a mobile phone or a Personal Digital Assistant (PDA), a media player, a gaming device or the like. The base stations communicate with the wireless device over a plurality of wireless channels coupled between the wireless device and the base stations (e.g., a downlink channel from a base station to a wireless device). The wireless device may send back information, including channel information, to the base stations over a plurality of feedback channels (e.g., an uplink channel from the wireless device to the base station).
The wireless device may include a transceiver coupled between an antenna and a baseband processor. The transceiver may comprise an amplifier and a first mixer coupled to a local oscillator. The amplifier is employed to convert a radio frequency voltage signal to a radio frequency current signal. The first mixer receives the signal from the amplifier and generates a signal at an intermediate frequency suitable for the baseband processor. After being processed by the first mixer, an in-phase (I) signal having the intermediate frequency is generated and sent to the baseband processor.
The transceiver further comprises a second mixer coupled to the local oscillator through a phase shifter. The phase shifter adds a 90 degree phase shift to the signal generated by the local oscillator. The second mixer generates a quadrature (Q) signal for digital signal processing in the baseband processor.
The wireless device often includes a front-end transconductance amplifier converting an input radio frequency voltage signal to a radio frequency current signal for driving the mixers. Programmable gain amplifiers are required to adjust the signal range so as to generate a suitable radio frequency current signal for the downstream devices.
It would be desirable to have a high performance amplifier exhibiting good behaviors such as high linearity, good compression performance, good gain step accuracy, low input impedance variations and the like under a variety of operating conditions.